Method of treating brine



Patented Mar. 17, 1931 UNED STATES PATENT QFFHQE WILLIAM R. COLLINGS, OF MIDLAND, 1\IICEIGAN, ASSIGNOR TO THE DOW CHEMICAL COMPANY, OF MIDZAND, lvZICHEGAIT, A COEPCBIATEQN SF MICHIGAN METHOD OF TREATING BRINE Application filed Septen ber 12, 1928. Serial No. 305,493.

In United States Letters Patent No. 1,627,068 to A. K. Smith and C. F. Prutton, dated May 3, 1927, there is disclosed animproved method or process for treating brines which contain calcium and magnesium chlorides, with the object of separating the latter from the former. Incidentally to such proccss the calcium and magnesium chlorides, at least in part, are crystallized out of the solution in the form of a double salt known as tachydrite (CaCl 2MgCl 12I-I O). These crystals are then separated from the mother liquor and by appropriate treatment the calcium chloride content thereof may be separated from the magnesium chloride and the latter purified.

One object of the present improved method of treating brine is to provide for more effective regulation of the steps leading up to the formation and separation of such tachydrite in the above described process. A further object is to facilitate the separation of.

the calcium chloride, andmagnesium chloride that compose such tachydrite.

To the accomplishment of the foregoing and related ends. the invention, then, consists of the steps hereinafter fully described and particularly pointed out in the claims, the annexed drawing and the following description illustrating and setting forth indetail certain steps embodying the invention, such disclosed means constituting, however, but several of the ways in which the principle of the invention may be used.

In said annexed drawing The single figure there appearing is a diagrammatic representationon the order of a flow sheet illustrating the apparatus and steps employed in carrying out the present improved process.

In the case of brine from the Midland, Michigan, field which contains, in addition to the hereinbefore mentioned constituents, traces of iron, bromine, etc, the brine will be preliminarily treated to separate such minor constituents. The brine is then received in a storage and settling tank 1 from which it is taken for the purpose of concentration to .an evaporator 2 where the salt (NaCl) is, eliminated, producing a B'e". solution, containing approximately 33 per cent. calcium chloride (CaCl and 11. per cent. magnesium chloride (MgCl which is stored in one or more tanks-3. Such solution is then further evaporated undervacuum in a second evaporator 4 with the formation of tachydrite crystals, substantially as described in the aforesaid Patent No. 1,627,068. These crystals, having a composition expressed by the formula CaCl .2l\IgCl .12H O as aforesaid, are thereupon separated from the mother liquor in a filter 5. The mother liquor of approximately ST-525 B. gravity, contains a largely increased proportion of calcium chlo ride to magnesium chloride over the original solution, its composition being roughly 53 per cent CaCl and 5 per cent Mgcl Such mother liquor is then treated with milk of lime in a mixing tank 6, whereby the magnesium chloride content thereof is precipitated as'magnesium hydrate. Such hydrate is separated in filter 7 and removed from the process, while the filtrate, which consists of a substantially pure solution of calcium chloride of approximately B. constitutes the calcium chloride product of the process and may be conducted to the calcium chloride finishing plant, not forming a part of the present system.

The tachydrite crystals from filter are washed to purify them from adherent mother liquor and dissolved either in situ or after being transferred to a dissolvin tank 8, in a limited amount of water with heating to a temperature of 90 to 100 C. Preferably this step is accomplished by direct introduction of steam into the mixture, which may be stirred to facilitate solution, and then SJillcient water is added to adjust the strength of the resulting solution, so that, when cooled to approximately 30 C., the gravity of the filtrate after separating the crystals found in such cooling is from 42.5" to 43 B. Experience has shown that when the solution is so adjusted, all of the calcium chloride remains dissolved at 30 (1, while aportion of the magnesium chloride content will separate out as pure crystals of the hexahydrate salt (MgCl; 6H O); At -t his sta-ge the solution contains approximately 27% MgCh and 16% CaCl before crystallization occurs.

The hot solution from 8 is drawn oil to a crystallizer 9, wherein it is cooled to approxi mately 30 C., whereupon crystals of magnesium chloride hexahydrate (MgChfiI-LO) are precipitated, while all of the calcium chloride remains in the solution. The crystals are separated from the solution in filter 10, washed free from adherent residual liquor, and, thus purified, constitutes the magnesium chloride product of the present process. If desired, these crystals may be further proc essed to reduce their water content. In such case they may be melted to produce a hot concentrated magnesium chloride solution which is evaporated down in a suitable finishing kettle. The filtrate from 10 containing approximately per cent. CaCl and. per cent. iilgCl with gravity of 43 lie. is returned to tank ()ther modes of applying the principle of my invention may be employed instead of the one explained, change being made as regards the method herein disclosed, provided the step or steps stated by any of the following claims or the equivalent of such stated step or steps be employed.

I therefore particularly point out and distinctly claim as my invention o 1. Ina method of treating a brine of the character described, the steps which consist in evaporating such brine to crystallize out the sodium chloride evaporating the residual brine containing calcium and magnesium chlorides to crystallize out the latter in the form of tachydrite and leave a mother liquor having a higher proportion of calcium chloride to magnesium chloride than the original brine; filtering out the tachydrite crystals; dissolving same in a limited amount of water; crystallizing n'iagucsium chloride heXahydrate from the resulting solution; separating such magnesium chloride crystals and returning the residual solution to the second step.

2. In a method of treating a brine of the character described, the steps which consist in evaporating such brine to crystallize out the sodium chloride; evaporating the residual rine containing calcium and magnesium chlorides to crystallize out the latter in the form of tachydrite and leave a mother liquor having a higher proportion'of calcium chloride to magnesium chloride than the original brine; separating such tachydrite and dissolving the same in a limited amount of water with addition of heat, whereby a solution is produced such that when cooled to approxi mately C. the filtrate remaining from the crystals thereupon formed will have a gravity of between 425 and 430 1%.

3. In a method of treating a brine of the character described, the steps which consist in evaporating such brine to crystallize out the sodium chloride; evaporating the residual brine containing calcium and magnesium chlorides to crystallize out the latter in the form of tachydrite and leave a mother liquor having a higher proportion of calcium chloride to magnesium chloride than the original brine; separating such tachydrite and dissolving the same in a limited amount of water with addition of heat, whereby a solution is produced such that when cooled to approximately 30 C. the filtrate remaining from the crystals thereupon formed will have a gravity of between 42.5 and 430 136., then cooling such solution to crystallize out magnesium chloride hexahydrate and separating the latter from the residual solution.

4. In a method of treating a brine of the character described, the steps which consist in evaporating such brine to crystallize out the sodium chloride; evaporating the residual brine containing calcium and magnesium chlorides to crystallize out the latter in the form of tachydrite and leave a mother liquor having a higher proportion of calcium chloride to magnesium chloride than the original brine; separating such tachydrite and dissolving the same in a limited amount of water with addition of heat, whereby a solution is produced such that when cooled to approximately 30 C. the filtrate remaining from the crystals thereupon formed will have a gravity of between 425 and 430 B.; then cooling such solution to crystallize out magnesium chloride hexahydrate; separating the latter from the residual solution and returning such solution to the second step.

In a method of treating a brine of the character described, the steps which consist in evaporating such brine to crystallize out the sodium chloride; evaporating the residual brine containing calcium and magnesium chlorides to crystallize out the latter in the form of tachydrite and leave a mother liquor having a higher proportion of calcium chloride tomagnesium chloride than the original brine; separating .such tachydrite; treating the mother liquor to separate the magnesium chloride content remaining therein; dissolving the tachydrite crystals in a limited amount of water with addition of heat, whereby a solution is produced such that when cooled to approximately 80 C. the filtrate remaining from the crystals thereupon formed will have a gravity of between 42.5 and 43.0 136.; then cooling such solution to crystallize out magnesium chloride hexahydrate; separating the latter from the residual solution and returning such solution to the second step.

6. In a method of separating calcium chloride from magnesium chloride in solution together, the steps which consist in evaporating such solution to crystallize out such chlorides in the form of tachydrite and leave a mother liquor having a higher proportion of calcium chloride to magnesium chloride than the original solution; separating such tachydrite and dissolving the same in a limited amount of water whereby a solution is pro ducedfrom which magnesium chloride heXa hydrate (MgChfiI-LO) will crystallize out and leave calcium chloride dissolved therein.

7. In a method of separating calcium chloride from magnesium chloride in solution together, the steps which consist in evaporating such solution to crystallize out such chlorides in the form of tachydrite and leave a mother liquor having a higher proportion of calcium chloride to magnesium chloride than the original solution; separating such tachydrite and dissolving the same in a limited amount of water, whereby a solution is produced from which magnesium chloride hexahydrate (MgChfiILO) will crystallize out and leave calcium chloride dissolved therein crystallizing out such heXahy-drate and returning the residual solution to the original mixture.

8. In a method of separating calcium chloride from magnesium chloride in solution together, the steps which consist in evaporating such solution to crystallize out such chlorides in the form of tachydrite and leave a mother liquor having a higher proportion of calcium chloride to magnesium chloride than the original solution; separating such tachydrite and dissolving same in a limited amount of water with addition of heat whereby a solution is produced such that when cooled to approximately 30 C. the filtrate remaining from the crystals thereupon formed will have a gravity of between 425 and 430 B.; then cooling such solution to crystallize out magnesium chloride hexahydrate and separating the latter from the residual solution.

9. In a method of separating calcium chloride from magnesium chloride in solution together, the steps which consist in evaporating such solution to crystallize out such chlorides in the form of tachydrite and leave a mother liquor having a higher proportion of calcium chloride to magnesium chloride than the original solution; separating such tachydrite and dissolving same in a limited amount of water with addition of heat whereby a solution is produced such that when cooled to approximately 30 C. the filtrate remaining from the crystals thereupon formed will have a gravity of between 425 to 43.0 B.; then cooling such solution to crystallize out magnesium chloride heXahydrate; separating such hexahydrate crystals from the residual solution and returning the latter to the original solution.

10. In a method of separating calcium chloride from magnesium chloride in solution together, the steps which consist in evaporating such solution to crystallize out such chlorides in the form of tachydrite and leave a mother liquor having a higher proportion ofcalciu-m chloride to magnesium chloride than the original solution;-separating such tachydrite; treating the mother liquor to separate the magnesium chloride content remaining therein and dissolving such taciydrite in a limited amount of water, whereby a solution is produced from which magnesium hexahydrate (MgCl .6H O) will crystallize out and leave calcium chloride dissolved therein.

11. In a method of separating calcium chloride from magnesium chloride in solution together, the steps which consist in evaporating such solution to crystallize out such chlorides in the form of tachydrite and leave a mother liquor having a higher proportion of calcium chloride to magnesium chloride than the original solution; separating such tachydrite; treating the mother liquor to separate the magnesium chloride content remaining therein; dissolving such tachydrite in a limited amount of water with addition of heat, where by a solution is produced such that when cooled to approximately 30 C. the filtrate remaining from the crystals thereupon formed will have a gravity of between 425 and 430 B.; then cooling such solution to crystallize out magnesium chloride hexahydrate and separating the latter from the residual solution.

12. In a method of separating calcium and magnesium chlorides from solutions containing the same which includes separating tachydrite crystals from a mother liquor having a higher proportion of calcium chloride to magnesium chloride than the original solution, the step which consists in dissolving such crystals in a limited amount of water with heating such that a solution is produced from which upon cooling to approximately 30 0. crystals of magnesium chloride hexahydrate will be precipitated and the filtrate remaining from the crystals will have a gravity of between 425 and 43 B.

13. In a method of separating calcium and magnesium chlorides from solutions containing the same which includes separating tachydrite crystals from a mother liquor having a higher proportion of calcium chloride to magnesium chloride than the original so lution, the steps which consist in dissolving such crystals in a limited amount of water with heating such that a solution is produced from which upon cooling to approxin'iately 30 0., crystals of magnesium chloride hexahydrate will be precipitated and the filtrate remaining from the crystals will have a gravity of 425 and 43 B., cooling such solution to crystallize out magnesium chloride hexahydrate crystals and separating such crystals from the residual solution.

Signed by me, this 10 day of September,

WILLIAM R. COLLINGS. 

